Semiconducting materials have proven to be the cornerstone of the electronics revolution; and silicon, thanks to its purity, ease of fabrication, and high yield in manufacturing, has been the dominant material utilized in integrated circuit technology. With the constant pressure for faster, more efficient devices, there is much interest in developing or identifying new, low-cost materials that can meet the interconnect demands associated with increasing parallelism and higher data rates. Additionally, pressure to reduce device size and density has focused efforts on identifying materials with improved heat dissipation and/or electrical conductivity characteristics.
The use of superconducting materials, in combination with established semiconductor technologies, has been proposed as a solution to the heat dissipation problems encountered with present-day semiconducting materials. Specifically, it has been suggested that superconducting wires and junctions could be used in integrated circuits to reduce heat dissipation. Unfortunately, even recently-discovered "high temperature" superconductors do not operate above cryogenic temperatures. Moreover, the expense and engineering difficulty associated with integration of available superconducting and semiconducting technologies make this possibility impractical, if not infeasible.
Optical communication systems offer a potential solution to the interconnect problem, but development efforts have been hampered by the difficulties associated with integrating efficient light sources into available silicon circuits. Silicon itself, like the other members of its periodic-table family (group IV), has limited optical capabilities due to its centrosymmetric crystal structure and an indirect band gap, which prohibits photon emission via efficient, band-to-band radiative transmission (see below).
Much effort has been directed at circumventing the selection rules that forbid band-to-band radiative transmission in indirect bandgap semiconductors, in order to develop semiconducting materials with improved optical properties (Iyer et al. Science 260:40-46, 1993). One approach has been to introduce suitable impurities into the group IV lattice. Tight binding of an exciton (an electron-hole pair) to an impurity can provide efficient radiative transmissions if a sufficient volume of impurities has been introduced. The most successful of these efforts have involved isoelectronic complexes and the rare-earth dopant Erbium. However, Erbium, like other radiative impurity complexes, is difficult to introduce in a concentration sufficient to provide optical gain.
Efforts have also been directed at growing ordered alloys and superlattices, with the idea of using band gap engineering to "fold" the Brillouin zone and achieve a quasi direct-gap material (Presting et al. Semicond. Sci. Technol. 7:1127-1148, 1992). The most popular of these materials systems has been silicon-germanium, with some recent interest in the quaternary alloy carbon-silicon-germanium-tin. These materials have yet to show the radiative efficiency found in direct bandgap materials.
A widely studied (but poorly understood) mechanism for light emission occurs in silicon that has undergone an electrochemical etching process (Iyer et al. supra). The etch produces a porous structure with nanometer-size particles that, upon passivation, provides efficient, visible photoluminescence. Samples of etched silicon have also been excited in electroluminescence, and have attracted some interest for display devices.
In addition, LEDs have been fabricated using silicon carbide. However, it has not been possible to produce optical amplifiers (e.g. lasers) using indirect bandgap materials for a discussion of the underlying reasons.
Thus, there is a need for development of materials with improved optical, electronic, and/or heat dissipation properties. There is a particular need for improved semiconductor materials. Preferably, the improved materials should be compatible with present-day electronic materials (e.g. silicon).